That is why you immediately are going to their ankles for control and sweeps. He really is unable to hit you in the face with the hands or elbows because your knees are in his chest and your body is straight. This is not a stopping position, but a transition to some sweeps. I will try to get some pics, since I am not doing a good job explaining it.

I saw something like this on a Barret Yoshida dvd.
He's in a similar position to the one you describe but controlling the arms,
he bends at the waist bringing the guy toward him at the same time he skips his hips out & pops on an armbar/triangle.

One of my training partners taught me a technique he got from a Marco Ruas DVD, where he basically jumps guard around the guys legs from either this position or open guard, and goes the heel hook. Your chances of escaping this are slim to none.

I'd work more on butterfly/X guard if I were you. Less chances of getting leg locked, better for controlling your opponent.

I use a variation of this to defend punches from the knees. You keep them at a distance as they press forward, then trap their arms, post a foot on the hip and upkick them with the other one. Unfortunately if the guy on top backs out before you have his arms you have to do something else since his forward pressure is actually maintaining the position.

As noted above, keep your feet on their hips to be ready for footlocks.